A kind of signal that demonstrates the best possible path to a destination in space and even provides motive power.

I don't think that this is the earliest use of this idea, but it's still worth looking at.

"Well," he said, "you saw for yourselves this was a hospital ship. It carried no crew. It was directed from a central guide-beam at Jupiter. The beam carried it from the Sol System here, where, because of a mechanical error, a meteor penetrated the protection screen and the ship crashed."

This is an interesting idea. For one thing, there really aren't any straight lines in space, at least for material objects going through the solar system; gravity fields and the constantly changing locations of the planets make direct "beams" difficult.